Organic transistor

ABSTRACT

An organic transistor having a source electrode, a drain electrode, a gate electrode, and an organic semiconductor layer, wherein the organic semiconductor layer comprises a compound represented by the following general formula [1] or [3]: 
     General Formula [1] 
     
       
         
         
             
             
         
       
         
         
           
             wherein A and B independently represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted aryl group.
 
General Formula [3]
 
           
         
       
    
     
       
         
         
             
             
         
       
         
         
           
             wherein R 1  to R 10  are independently a hydrogen atom, a halogen atom, an alkyl group which has 4 or less carbon atoms and may be substituted with a halogen atom, an alkoxyl group which has 4 or less carbon atoms and may be substituted with a halogen atom, an amino group which has 4 or less carbon atoms and may be substituted with a halogen atom, a nitro group, or a cyano group, and the compound contains at least one halogen atom.

TECHNICAL FIELD

The present invention relates to an organic thin film transistor formedby the use of an organic semiconductor.

BACKGROUND ART

Field effect transistors (FETs) have widely been used as importantswitching devices or amplifying devices as well as bipolar transistors.Hitherto, transistors using silicon, and others have been put intopractice, and applied to wide fields. A field effect transistor exhibitscharacteristics thereof by controlling the transportation of carriers inits semiconductor layer present between its source electrode and itsdrain electrode by the use of its gate electrode with an insulatinglayer interposed therebetween. The field effect transistor is called ann type in a case where the carriers are electrons, and called a p typein a case where the carriers are holes (a monopolar device). In contrastto the monopolar device, the field effect transistor capable oftransporting both of electrons and holes is called a bipolar device.

In particular, devices wherein a metal oxide is used in an insulatinglayer, which are called MOS (metal oxide semiconductor) structures, arewidely applied to logical gate devices, inverter circuits, memorydevices, and others. Of the devices, well known are MOS-FETs having athermally oxidized film of silicon dioxide on silicon.

About inorganic semiconductor devices, a typical example of which is Si,highly complicated producing steps are repeated many times; thus,enormous costs are required for the production thereof. Moreover, theproduction includes a step of high-temperature treatment; therefore, itis difficult to use a flexible plastic substrate or an organicsemiconductor. In comparison thereto, in the case of organictransistors, an device using a plastic substrate can be produced. Thus,the organic transistors are expected as flexible and light transistors.

In recent years, attention has been paid to devices wherein organicmaterial is used in an active layer, such as organic ELs, organiclasers, organic solar cells, and organic transistors. Advantages basedon the use of organic material include advantages that various materialscan be designed and many added values can be given. In the case ofgiving an organic transistor as an example, the following advantages arementioned: high temperature treatment, which is essential forconventional Si processes, is not required; therefore, organictransistor can be fabricated on a plastic substrate, and added valuesthat the transistor is flexible and light and is not easily broken canbe given. Moreover, the production process can be made very simple andeasy, and a semiconductor material soluble in a solvent can be yieldedin accordance with material design. This makes it possible to applythereto a printing process such as screen printing or inkjet printing.Thus, from the viewpoint of productivity and costs, organicsemiconductors are very advantageous as compared with inorganicsemiconductors.

The operation characteristics of field effect transistors are largelyrelative to the electrostatic capacity of their insulating layer, theirdevice structures (channel length and channel width), and the carriermobility of their semiconductor layer. In organic semiconductormaterials, the development of materials having a high mobility has beenactively made. Additionally, the development of organic semiconductormaterials high in stability has also become important since there hasbeen caused a problem of deterioration in device characteristics basedon a change with the passage of time.

Patent Document 1: Japanese Patent Application Laid-Open No. 2001-94107

Patent Document 2: Japanese Patent Application Laid-Open No. 2002-198539

Non-Patent Document 1: Applied Physics Letters, 2001, vol. 78, p. 228

Non-Patent Document 2: Advanced Materials, 1999, vol. 11, p. 480

DISCLOSURE OF THE INVENTION

An object of the invention is to provide an organic transistor that thedevice can be more simply and easily produced than inorganicsemiconductor devices and further transistor characteristics are stablefor a long term and a producing process thereof.

The invention relates to an organic transistor having a sourceelectrode, a drain electrode, a gate electrode, and an organicsemiconductor layer, wherein the organic semiconductor layer comprises acompound represented by the following general formula [1]:

wherein A and B independently represent a substituted or unsubstitutedalkyl group, a substituted or unsubstituted heterocyclic group, or asubstituted or unsubstituted aryl group.

The invention also relates to the organic transistor wherein A and B areindependently represented by the following general formula [2]:

wherein R¹ to R³ independently represent a hydrogen atom, a halogenatom, a substituted or unsubstituted alkyl group, a substituted orunsubstituted heterocyclic group, a substituted or unsubstituted arylgroup, a substituted or unsubstituted alkoxy group, a substituted orunsubstituted heterocyclic oxy group, a substituted or unsubstitutedaryloxy group, an alkylthio group, an arylthio group, a heterocyclicthio group, an alkylsulfonyl group, an arylsulfonyl group, aheterocyclic sulfonyl group, or a substituted or unsubstituted aminogroup; and substituents of R¹ to R³ may be bonded to each other to forma cycloalkyl ring, a heterocyclic ring, or an aromatic hydrocarbon ring.

The invention also relates to the organic transistor having a sourceelectrode, a drain electrode, a gate electrode, and an organicsemiconductor layer, wherein the organic semiconductor layer comprises acompound represented by the following general formula [3]:

wherein R¹ to R¹⁰ are independently a hydrogen atom, a halogen atom, analkyl group which has 4 or less carbon atoms and may be substituted witha halogen atom, an alkoxy group which has 4 or less carbon atoms and maybe substituted with a halogen atom, an amino group which has 4 or lesscarbon atoms and may be substituted with a halogen atom, a nitro group,or a cyano group, and the compound contains at least one halogen atom.

The invention also relates to the organic transistor wherein R7 to R¹⁰are independently a hydrogen atom, or a halogen atom.

The invention also relates to the organic transistor wherein the halogenatom is a fluorine atom.

The invention also relates to the organic transistor having the sourceelectrode, the drain electrode, the gate electrode, and the organicsemiconductor layer, wherein the organic semiconductor layer is formedby vacuum vapor-deposition at a vapor-deposition rate of 1 nm/sec orless.

The invention also relates to the organic transistor further having agate insulating film.

Furthermore, the invention relates to a process for producing an organictransistor having a source electrode, a drain electrode, a gateelectrode, and an organic semiconductor layer, including the step ofsubjecting a compound represented by the general formula [1] or [3] tovacuum vapor-deposition or spin coating, thereby forming an organicsemiconductor layer.

The invention also relates to the process for producing an organictransistor wherein the organic semiconductor layer is formed by thevacuum vapor-deposition wherein the rate of the vapor-deposition is setto 1 nm/sec or less.

The invention also relates to the process for producing an organictransistor wherein R⁷ to R¹⁰ are independently a hydrogen atom or ahalogen atom.

The invention also relates to the process for producing an organictransistor wherein the halogen atom is a fluorine atom.

The invention also relates to the process for producing an organictransistor wherein the transistor further has a gate insulating film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows conception diagrams illustrating an embodiment of thestructure of the organic transistor of the invention.

FIG. 2 is a graph showing an example of the relationship betweenwavelength and the absolute value of retardation.

REFERENCE SYMBOLS

-   A source electrode(s) or drain electrode(s)-   B gate electrode(s)-   C organic semiconductor layer-   D gate insulating layer-   E substrate

BEST MODE FOR CARRYING OUT THE INVENTION

The invention is characterized in that an organic semiconductor layerwhich is one of constituting elements of a transistor contains acompound represented by the following general formula [1]:

wherein A and B independently represent a substituted or unsubstitutedalkyl group, a substituted or unsubstituted heterocyclic group, or asubstituted or unsubstituted aryl group.

The invention also relates to the organic transistor wherein A and B inthe general formula [1] are independently represented by the followinggeneral formula [2]:

wherein R¹ to R³ independently represent a hydrogen atom, a halogenatom, a substituted or unsubstituted alkyl group, a substituted orunsubstituted heterocyclic ring, a substituted or unsubstituted arylgroup, a substituted or unsubstituted alkoxy group, a substituted orunsubstituted heterocyclic oxy group, a substituted or unsubstitutedaryloxy group, an alkylthio group, an arylthio group, a heterocyclicthio group, an alkylsulfonyl group, an arylsulfonyl group, aheterocyclic sulfonyl group, or a substituted or unsubstituted aminogroup; and substituents of R¹ to R³ may be bonded to each other to forma cycloalkyl ring, a heterocyclic ring, or an aromatic hydrocarbon ring.

A and B in the compound represented by the general formula [1] in theinvention independently represent a substituted or unsubstituted alkylgroup, a substituted or unsubstituted heterocyclic group, or asubstituted or unsubstituted aryl group.

R¹ to R³ in the compound represented by the general formula [2] in theinvention independently represent a hydrogen atom, a halogen atom, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedheterocyclic ring, a substituted or unsubstituted aryl group, asubstituted or unsubstituted alkoxy group, a substituted orunsubstituted heterocyclic oxy group, a substituted or unsubstitutedaryloxy group, an alkylthio group, an arylthio group, a heterocyclicthio group, an alkylsulfonyl group, an arylsulfonyl group, aheterocyclic sulfonyl group, or a substituted or unsubstituted aminogroup; and substituents of R¹ to R³ may be bonded to each other to forma cycloalkyl ring, a heterocyclic ring, or an aromatic hydrocarbon ring.

The substituted or unsubstituted alkyl group in the invention may be alinear or branched alkyl group such as a methyl, ethyl, propyl, butyl,sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, stearyl,2-phenylisopropyl, trichloromethyl, trifluoromethyl, benzyl,α-phenoxybenzyl, α,α-dimethylbenzyl, α,α-methylphenylbenzyl,α,α-ditrifluoromethylbenzyl, triphenylmethyl, or α-benzyloxybenzylgroup. The cyclic alkyl group (cycloalkyl ring) may be a cyclobutyl,cyclopentyl, cyclohexyl, cycloheptyl or cyclooctyl group, or any othercycloalkyl group.

The heterocyclic group in the invention may be a heterocyclic group in amonocyclic form, or a heterocyclic group in a condensed polycyclic form.

Examples of the monocyclic-form heterocyclic group include thienyl,furyl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl,pyridazinyl, triazinyl, triazolyl, oxazolyl, thiazolyl, oxadiazolyl,thiadiazolyl, and imidadiazolyl groups.

Examples of the condensed-polycyclic-form heterocyclic group includeindolyl, quinolyl, isoquinolyl, phthalazinyl, quinoxalinyl,quinazolinyl, carbazolyl, acridinyl, phenazinyl, benzofuryl,isothiazolyl, isoxazolyl, furazanyl, phenoxazinyl, benzothiazolyl,benzooxazolyl, benzoimidazolyl, benzotriazolyl, and pyranyl groups.Other examples of the condensed polycyclic group include 1-tetralyl,2-tetralyl, and tetrahydroquinolyl groups.

The aryl group may be a monocyclic aryl group or a condensed polycyclicaryl group.

An example of the monocyclic aryl group is a phenyl group.

Examples of the condensed polycyclic aryl group include naphthyl,anthryl, phenanthryl, fluorenyl, acenaphthyl, azulenyl, heptalenyl,pyrenyl, perylenyl, and triphenylenyl groups.

In the invention, the heterocyclic group or aryl group may be a groupwherein two or more heterocyclic groups (monocyclic-form heterocyclicgroups or condensed-polycyclic-form heterocyclic groups) and/or arylgroups (monocyclic aryl groups or condensed polycyclic aryl groups) arelinked with each other via one or more non-aromatic-ring structuralunits containing one or more atoms selected from carbon, hydrogen,oxygen, nitrogen and sulfur atoms.

The non-aromatic-ring structural unit containing one or more atomsselected from carbon, hydrogen, oxygen, nitrogen and sulfur atoms is alinear, branched or cyclic unit having a bivalence or higher valence,and containing no aromatic ring (heterocyclic group nor aryl group). Theunit preferably has 1 to 40 atoms. Examples of the non-aromatic-ringstructural unit include oxygen and sulfur atoms; and carbonyl, sulfonyl,sulfinyl, alkyl, alkenyl, alkyloxy, alkylthio, cycloalkyl, amino,alkylamino groups, and other residues.

In a case where heterocyclic rings or aryl groups are linked with eachother directly or via a non-aromatic-ring structural unit, the number ofthe heterocyclic rings or aryl groups is from 2 to 10. Each of theheterocyclic rings or aryl groups may be bonded at its two or moresites. The heterocyclic rings or aryl groups may be acondensed-polycyclic-form heterocyclic group or a condensed polycyclicaryl group, and their monocycle and their condensed ring may be bondedto each other.

Examples of one or more substituents which the heterocyclic group oraryl group has include halogen atoms; and alky, alkoxy, aryl, aryloxy,heterocyclic oxy, sulfonyl, amino, and cyano groups. The substituentsmay be bonded to each other to form a ring.

Specifically, the group wherein two or more heterocyclic groups or arylgroups are bonded directly to each other is, for example, a residuehaving a structure of binaphthyl, biquinoline, flavone, phenyltriazine,bisbenzothiazol, bithiophene, thienylbenzene, phenylbenzotriazole,phenylbenzimidazole, phenylacridine, bis(benzooxazolyl)thiophene,bis(phenyloxazolyl)benzene, biphenylylphenyloxadiazole,diphenylbenzoquinone, diphenylisobenzofurane, diphenylpyridine,dibenzyl, or diphenylfluorene.

The group wherein two or more heterocyclic groups or aryl groups arebonded to each other via a non-aromatic-ring structural unittherebetween is, for example, a residue having a structure of dibenzylnaphthyl ketone, dibenzilidenecyclohexanone, stylbene,distyrylnaphthalene, (phenylethyl)benzylnaphthalene, diphenyl ether,dimethyldiphenylamine, benzophenone, phenyl benzoate, diphenylurea,diphenylsulfide, diphenylsulfone, diphenoxybiphenyl,bis(phenoxyphenyl)sulfone, diphenylmethane, bis(phenylisopropyl)benzene,bis(phenoxyphenyl)propane, diphenylhexafluoropropane, diphenoxybenzene,ethylene glycol diphenyl ether, neopentyl glycol diphenyl ether,dipicolylamine, dipyridylamine, or triphenylamine.

The condensed polycyclic aryl group is preferably a condensed polycyclicaryl group having 10 to 40 carbon atoms, or a group wherein 2 to 10 arylgroups including at least one condensed polycyclic aryl group having 10to 40 carbon atoms are linked directly to each other. Specific examplesthereof include naphthalene, anthracene, phenanthrene, fluorene, pyrene,chrysene, naphthacene, pentacene, perylene, azulene, coronene, rubicene,decacyclene, 1,1-binaphthalene, and 9,9-bianthracene.

Specific examples of the halogen atoms include fluorine, chlorine,bromine, and iodine.

Examples of the substituted or unsubstituted alkoxy group includemethoxy, ethoxy, propoxy, n-butoxy, tert-butoxy, hexyloxy, n-octyloxy,tert-octyloxy, 2,2,2-trifluoroethoxy, and benzyloxy groups.

Examples of the substituted or unsubstituted aryloxy group includephenoxy, biphenyloxy, naphthoxy, binaphthyloxy, methylphenoxy,dihexylphenoxy, diphenylaminophenoxy, octylphenoxy, cyanonaphthoxy, andchloroanthranyloxy groups.

Examples of the substituted or unsubstituted heterocyclic oxy groupinclude thienyloxy, furyloxy, pyrroleoxy, bithienyloxy, quinolyloxy,phenylthienyloxy, pyridyloxy, and thienothienyloxy groups.

Examples of the substituted or unsubstituted amino group include amino,dimethylamino, diethylamino, N-methyl-N-phenylamino, diphenylamino,ditolylamino, and dibenzylamino groups.

The substituents may be bonded to each other to form a substituted orunsubstituted cyclopentene, cyclohexene, phenyl, naphthalene,anthracene, pyrene, fluorene, furan, thiophene, pyrrole, oxazole,thiazole, imidazole, pyridine, pyrazine, pyrroline, pyrazoline, indole,quinoline, quinoxaline, xanthene, carbazole, acridine or phenanthrolinering, or the like.

Typical examples of the compound of the general formula [1] in theinvention are specifically illustrated as exemplified compounds (1) to(71); however, the compound is not limited thereto. In the exemplifiedcompounds, Me, Et and Hex represent a methyl group, an ethyl group, anda hexyl group, respectively.

The exemplified compounds may be synthesized in accordance withsynthesizing methods disclosed in, for example, U.S. Pat. No. 4,579,949.

In the invention, for example, the exemplified compound (1) issynthesized as follows:

Into 500 g of amyl alcohol were dissolved 11.4 g of dimethyl succinate,30.1 g of 3-chlorobenzonitrile, and 21.1 g of sodium butoxide, and thenthe solution was refluxed for 6 hours. The solution was cooled, and thenthe precipitation was filtrated and washed with acetic acid and methanolto yield 30.3 g of the exemplified compound (1).

The invention is also characterized in that an organic semiconductorlayer which is one of the constituents of a transistor contains acompound represented by the following general formula [3]:

wherein R¹ to R¹⁰ are independently a hydrogen atom, a halogen atom, analkyl group which has 4 or less carbon atoms and may be substituted witha halogen atom, an alkoxyl group which has 4 or less carbon atoms andmay be substituted with a halogen atom, an amino group which has 4 orless carbon atoms and may be substituted with a halogen atom, a nitrogroup, or a cyano group, and the compound contains at least one halogenatom.

R¹ to R¹⁰ in the compound represented by the general formula [3] in theinvention are independently a hydrogen atom, a halogen atom, an alkylgroup which has 4 or less carbon atoms and may be substituted with ahalogen atom, an alkoxyl group which has 4 or less carbon atoms and maybe substituted with a halogen atom, an amino group which has 4 or lesscarbon atoms and may be substituted with a halogen atom, a nitro group,or a cyano group, and the compound contains at least one halogen atom.

Specific examples of the halogen atom in the invention include fluorine,chlorine, bromine, and iodine.

Examples of the alkyl group, which has 4 or less carbon atoms and may besubstituted with a halogen atom, in the invention include methyl, ethyl,propyl, isopropyl, butyl, sec-butyl, tert-butyl, fluoromethyl,difluoromethyl, trifluoromethyl, chloromethyl, trichloromethyl,dichloromethyl, bromomethyl, dibromomethyl, iodomethyl,pentafluoroethyl, 2,2,2-trifluoroethyl, 2-fluoroethyl, 2-iodoethyl,perfluoropropyl, perfluoroisopropyl,2,2,2-trifluoro-(1-trifluoromethyl)ethyl, 2-bromopropyl, 3-iodopropyl,perfluorobutyl, perfluoro-tert-butyl, 2,2,3,3,4,4,4-heptafluorobutyl,2-iodo-1 methylpropyl, 4-chlorobutyl, 2-chloro-3-fluoropropyl, and1,2-dichloro-3-iodobutyl groups.

Examples of the alkoxyl group which has 4 or less carbon atoms and maybe substituted with a halogen atom in the invention include methoxy,ethoxy, propoxy, isopropoxy, n-butoxy, tert-butoxy, fluoromethoxy,difluoromethoxy, trifluoromethoxy, chloromethoxy, trichloromethoxy,dichloromethoxy, bromomethoxy, dibromomethoxy, iodomethoxy,pentafluoroethoxy, 2,2,2-trifluoroethoxy, 2-fluoroethoxy, 2-iodoethoxy,perfluoropropoxy, perfluoroisopropoxy,2,2,2-trifluoro-(1-trifluoromethyl)ethoxy, 2-bromopropoxy,3-iodopropoxy, perfluorobutoxy, perfluoro-tert-butoxy,2,2,3,3,4,4,4-heptafluorobutoxy, 2-iodo-1 methylpropoxy, and4-chlorobutoxy groups.

Examples of the amino group which has 4 or less carbon atoms and may besubstituted with a halogen atom include amino, monomethylamino,dimethylamino, N-methyl-N-ethylamino, diethylamino,N-methyl-N-propylamino, monotrifluoromethylamino,ditrifluoromethylamino, dichloromethylamino,N,N-bis(trifluoromethyl)amino, N,N-bis(pentafluoroethyl)amino,chloromethylamino, N-trifluoromethyl-N-propylamino, andN,N-di(chloroethyl)amino groups.

Typical examples of the compound of the general formula [3] in theinvention are specifically illustrated below as exemplified compounds(100) to (256). However, the compound is not limited thereto. In theexemplified compounds, Me, Et, Pr and tert-Bu represent a methyl group,an ethyl group, a n-propyl group, and a tert-butyl group, respectively.

The use of the compound represented by the general formula [1] or [3] inan active layer (organic semiconductor layer) of an organic transistordevice makes it possible to provide a transistor that is lessdeteriorated by a change thereof with the passage of time. For aspecific structure and specification of an organic transistor whereinthe active layer can be used, those of any known organic transistor maybe used.

Preferred examples of the structure include structures I to Xillustrated in FIG. 1.

In FIG. 1, “A” represents a source electrode or a drain electrode (oneof the two electrodes is a source electrode and the other is a drainelectrode). “B” represents a gate electrode, “C” represents an organicsemiconductor layer, “D” represents a gate insulating layer, and “E”represents a substrate. In FIG. 1, II, IV, VI and VIII, a substrate alsofunctions as its gate electrode.

In order to use the compound represented by the general formula [1] or[3] as an active layer of an organic transistor device, vacuumvapor-deposition is preferable to form a film on a substrate. By heatingthe substrate beforehand in this case, characteristics thereof can alsobe improved. By using a solution wherein the compound is dissolved in anappropriate organic solvent, a film can be formed on a substrate bymeans of spin coating, drop casting, ink-jetting, screen printing or thelike. Spin coating is preferable to form a film.

When the film is formed by vacuum vapor-deposition, the vapor-depositionrate is preferably 1 nm/sec or less, more preferably 0.5 nm/sec or less,even more preferably 0.1 nm/sec or less.

The state of the organic semiconductor layer formed on the substrate asdescribed above may be evaluated as follows:

Ellipsometry is a method that a change in the polarization state thereofis observed when light is reflected or transmitted in a substance, andoptical constants (the refractive index and the extinction coefficient)is determined. By processing the obtained data, the film thickness andthe refractive index of the thin film can be calculated.

In the invention, it is supposed that about any organic semiconductorthin film represented by the general formula [3], incident light isdivided into a polarized light parallel to the surface onto which theincident light is radiated, and a polarized light perpendicular to thesurface. After incident light transmitted an organic semiconductor thinfilm, a device for measuring a change in the polarization state(ellipsometer) was used to measure the retardation of each of thepolarized lights. The measuring wavelength at this time was set to 650nm, which is not absorbed by the compound, and the incident angle of theincident light was set to 45 degrees.

The phenomenon has not been analyzed yet in detail; however, in theinvention, it has been understood that the relationship between theretardations of the polarized lights and the vapor-deposition rate isthat: as the vapor-deposition rate is smaller, the absolute values ofthe retardations become larger and further the stability of thetransistor increases.

At present, it is assumed that this is probably related to thearrangement or orientation of molecules in the thin film. Experimentalresults demonstrate that when the absolute values of the retardations ofthe polarized lights at 650 nm are 1 degree or more, preferably 3degrees or more, transistors excellent in stability over time areobtained, and when the values are up to about 1 degrees, transistorshave excellent stability over time. However, it is considered that whenthe values are more than 10 degrees (for example, about 15 degrees),transistor keeps the excellent stability over time.

As the substrate, a glass substrate or a silicon substrate may be used.From the viewpoint of lightness and flexibility, a plastic film may beused, for example, polyethylene, polyethylene terephthalate,polyethylene naphthalate, polyethersulfone, polypropylene, polyimide,polycarbonate, and cellulose triacetate. Depending on the structure ofthe device, the substrate itself may also function as an electrode. Inthis case, the characteristics can be improved by heating the substrate.

During the formation of the film, the temperature of the substrate maybe room temperature, and ranges preferably from 50 to 250° C., morepreferably from 70 to 200° C., even more preferably from 70 to 150° C.

In the invention, the material for the source electrode, the drainelectrode and the gate electrode is not particularly limited as long asthe material is an electroconductive material. Specifically, gold,platinum, palladium, aluminium, indium, calcium, potassium, magnesium,tin, lead, indium/tin oxide (ITO), silver paste, carbon paste, graphite,glassy carbon, lithium, lithium fluoride/aluminum laminate,calcium/aluminum laminate, silicon, ruthenium, manganese, yttrium andtitanium; and alloys thereof. However, the material is not limited tothese materials. Typical examples of the alloys includemagnesium/silver, magnesium/indium, and lithium/aluminium. However, thealloys are not limited thereto. The ratio in each of the alloys iscontrolled by the temperature of the vapor-deposition source, theatmosphere, the vacuum pressure, and others, and is selected into anappropriate ratio. The source electrode, the drain electrode, and thegate electrode may each be formed into a structure of two or more layersif necessary. Furthermore, an electroconductive electrode which uses anorganic material, for examples, electroconductive polypyrrole,electroconductive polythiophene, electroconductive polyaniline, andPEDOT/PSS, can be used.

As a process for fabricating the electrodes, any process, for examples,dry film-fabricating processes such as vacuum vapor-deposition,sputtering, plasma, and ion plating, and wet film-fabricating processessuch as spin coating, dipping, and flow coating may be conducted. Theelectrodes may each be formed by using a coated film with lithography,laser ablation, or the like.

An electrode surface may be modified with a self-assembled monolayer(SAM) to lower the surface energy of the electrode and improve thecrystal growth or the crystal arrangement of the organic semiconductormaterial, the wettability between the organic semiconductor material andthe electrode, and others. In the case of using, for example, a goldelectrode, surface-modification with an alkane thiol is preferable.

As the gate insulating layer, various insulating layers may be used. Aninorganic oxide having a high dielectric constant is particularlypreferred. Examples of the inorganic oxide include silicon oxide,aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadiumoxide, barium strontium titanate, barium zirconate titanate, leadzirconate titanate, lead lanthanum titanate, strontium titanate, bariumtitanate, barium magnesium fluoride, bismuth titanate, strontium bismuthtitanate, strontium bismuth tantalate, bismuth tantalate niobate, andtrioxide yttrium. More preferred are silicon oxide, aluminum oxide,tantalum oxide and titanium oxide. An inorganic nitride such as siliconnitride and aluminum nitride can be preferably used.

The method for forming the gate insulating film may be a dry processsuch as vacuum vapor-deposition, the molecular beam epitaxial growingmethod, the ion cluster beam method, the low-energy ion beam method, ionplating, CVD, sputtering, or the atmospheric plasma method, or a wetprocess such as spray coating, spin coating, blade coating, dip coating,casting, roll coating, bar coating, die coating, any other paintingmethod, or a method based on patterning, such as printing orink-jetting. In accordance with the raw material, an appropriate methodmay be used.

The wet process may be a method of painting a liquid wherein fineparticles of an organic oxide are dispersed in any organic solvent orwater by an optional use of a dispersion aid such as a surfactant, andthen drying the painted liquid, or the so-called sol-gel method that asolution of an oxide precursor, such as an alkoxy compound, is paintedand dried.

A hydrophilic gate insulating film can be changed from hydrophilicity tohydrophobicity by subjecting the film to a chemical surface treatmentthat may be of various types. This improves the wettability between thegate insulating film and the hydrophobic organic semiconductor layer andthe crystallinity of the semiconductor material. An advantageous effectthat a current leakage is decreased is also provided. As a typicalsurface treatment material, a silane material is preferred, forexamples, hexamethyldisilazane (HMDS), octyltrichlorosilane (OTS),7-octenyltrichlorosilane (VTS),tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FTS), andbenzyltrichlorosilane (BTS). However, the surface treatment material isnot limited thereto.

An organic gate insulating film may be polyethylene, polyvinyl chloride,polyimide, polyamide, polyester, polyvinyl phenol, polyvinyl alcohol,novolak resin, cyanoethylpullulan, polyacrylonitrile, parylene, or thelike. Copolymers thereof may be used.

According to the invention, it is possible to provide an organictransistor device having both of an excellent ON/OFF ratio and a highstability over time.

Hereinafter, the invention will be more specifically described by theexamples; however, the invention is not limited thereby.

EXAMPLES Example 1

Compounds represented by the general formula [1] were each used as anorganic semiconductor material to produce organic transistor devices 1to 46 independently by the following two methods:

(1) Dry Process

A thermally oxidized layer was formed as a gate insulating layer on a Siwafer having a resistivity of 0.02 Ωcm as a gate electrode. Thereafter,the resultant was surface-treated with hexamethyldisilazane (HMDS). Byvacuum vapor-deposition (vacuum pressure: 2.2×10⁻⁶ Torr,vapor-deposition rate: 0.05 nm/sec), some compounds shown in Table 1were each stacked thereon into a thickness of 70 mm. Furthermore, a maskwas used to vapor-deposit gold onto the surface of this film to form asource electrode and a drain electrode. In this way, an organictransistor device was produced wherein the film thickness of the sourceelectrode and the drain electrode was 300 nm, the channel width (W) was5 mm, and the channel length (L) was 20 μm.

(2) Wet Process

A substrate treated in the same way as in the case of the vacuumvapor-deposition was used, and a spin coater was used, thereon, asolution of each of some compounds shown in Table 1 in toluene (orDMSO). The resultant was naturally dried in ambient temperature to forma semiconductor layer (thickness: 100 nm), and further the resultant wasthermally treated at 80° C. for 30 minutes under nitrogen atmosphere.Furthermore, a mask was used to vapor-deposit gold onto the surface ofthis semiconductor layer to form a source electrode and a drainelectrode. In this way, an organic transistor device was fabricatedwherein the film thickness of the source electrode and the drainelectrode was 300 nm, the channel width (W) was 5 mm, and the channellength (L) was 20 μm.

Comparative Examples 1 to 3

Instead of the compound of the invention, compounds A to C illustratedbelow were each used as an organic semiconductor material to produceorganic transistor devices independently in the same way as inExample 1. The used compound C had a weight-average molecular weight of48,300 (in terms of polystyrene, GPC).

The organic transistor devices produced as described above were eachused, and the transistor device was stored at 40° C. in the atmosphere.Changes in the transistor characteristic of the device with the passageof time were compared. A voltage of 30 V or −30 V was applied betweenthe source electrode and the drain electrode, and a sweep of voltagesranging from 50 to −50 V was made onto the gate electrode. The ratio ofthe maximum current value (ON current) between the source electrode andthe drain electrode at this time to the minimum current value (OFFcurrent) was defined as the ON/OFF ratio. About each of the devices, theON/OFF ratio just after the formation of the device was regarded as one.In this case, the relative value of the ON/OFF ratio after one day, thatafter one week, and that after one month are as described below.

TABLE 1 Semiconductor Organic layer Relative value of the ON/OFF ratioElement semiconductor manufacturing One month No. material method Oneday later One week later later  1 Compound(1) Dry process 0.99 0.94 0.92 2 Compound(2) Dry process 0.97 0.93 0.93  3 Compound(4) Dry process0.94 0.95 0.93  4 Compound(5) Dry process 0.93 0.88 0.82  5 Compound(6)Dry process 0.94 0.87 0.80  6 Compound(7) Dry process 0.98 0.92 0.90  7Compound(9) Dry process 0.99 0.96 0.94  8 Compound(10) Dry process 0.940.88 0.81  9 Compound(11) Dry process 0.98 0.94 0.91 10 Compound(12) Dryprocess 0.94 0.91 0.83 11 Compound(13) Dry process 0.96 0.89 0.87 12Compound(15) Dry process 0.99 0.97 0.97 13 Compound(17) Dry process 0.960.92 0.89 14 Compound(19) Dry process 0.97 0.93 0.91 15 Compound(19) Wetprocess 0.93 0.91 0.88 16 Compound(21) Dry process 0.96 0.87 0.82 17Compound(24) Dry process 0.93 0.84 0.80 18 Compound(27) Dry process 0.970.89 0.88 19 Compound(28) Dry process 0.98 0.93 0.90 20 Compound(30) Dryprocess 0.97 0.94 0.91 21 Compound(33) Dry process 0.99 0.97 0.92 22Compound(33) Wet process 0.97 0.91 0.87 23 Compound(36) Dry process 0.960.84 0.81 24 Compound(41) Dry process 0.98 0.95 0.90 25 Compound(42) Dryprocess 0.94 0.95 0.93 26 Compound(45) Dry process 0.96 0.91 0.88 27Compound(46) Dry process 0.99 0.93 0.91 28 Compound(46) Wet process 0.940.91 0.89 29 Compound(47) Dry process 0.96 0.92 0.89 30 Compound(47) Wetprocess 0.94 0.91 0.87 31 Compound(51) Dry process 0.96 0.92 0.89 32Compound(52) Dry process 0.96 0.97 0.95 33 Compound(53) Dry process 0.970.91 0.87 34 Compound(57) Dry process 0.96 0.88 0.82 35 Compound(59) Dryprocess 0.90 0.84 0.83 36 Compound(60) Dry process 0.97 0.93 0.92 37Compound(60) Wet process 0.94 0.90 0.89 38 Compound(61) Wet process 0.970.93 0.92 39 Compound(63) Wet process 0.94 0.88 0.82 40 Compound(64) Dryprocess 0.97 0.92 0.89 41 Compound(66) Dry process 0.96 0.91 0.90 42Compound(66) Wet process 0.96 0.89 0.87 43 Compound(67) Wet process 0.980.90 0.87 44 Compound(68) Wet process 0.96 0.91 0.90 45 Compound(69) Wetprocess 0.98 0.93 0.91 46 Compound(70) Dry process 0.97 0.90 0.90Comparative Compound A Dry process 0.88 0.63 0.41 Example 1 ComparativeCompound B Dry process 0.89 0.43 0.22 Example 2 Comparative Compound CWet process 0.90 0.34 0.30 Example 3

Comparative Example

According to Table 1, it is understood that the organic transistordevices for an active layer produced by the use of the semiconductormaterial of the invention also exhibit high stability over time in theatmosphere.

Example 2

Compounds represented by the general formula [3] were each used as anorganic semiconductor material to produce organic transistor devices 47to 81 independently as follows:

First, Synthesis examples in the invention are described below.Symmetric ones out of the exemplified compounds can be synthesized by,for example, synthesis methods disclosed in the specification of U.S.Pat. No. 4,579,949.

Synthesis Example 1

18.4 g of dimethyl succinate, 53.1 g of 4-trifluoromethylbenzonitrile,and 25.3 g of sodium butoxide were dissolved into 200 g of amyl alcohol,and then the solution was refluxed for 8 hours. The solution was cooled,and then the precipitation was filtrated and washed with acetic acid andmethanol to yield 21.2 g of an exemplified compound (105). By massspectrometry based on MALDITOF-MS (autoflex II, manufactured by BrukerDaltonics Inc.), the result was consistent with the molecular weight(Calcd.: 424.06, Found: 423.88) of the compound (105).

Synthesis Example 2

An exemplified compound (116) was yielded in the same way as inSynthesis Example 1 except that 4-fluorobenzonitrile was used instead of4-trifluoromethylbenzonitrile. By mass spectrometry based onMALDITOF-MS, the result was consistent with the molecular weight(Calcd.: 324.07, Found: 324.25) of the compound (116).

Synthesis Example 3

An exemplified compound (121) was yielded in the same way as inSynthesis Example 1 except that 3,5-difluorobenzonitrile was usedinstead of 4-trifluoromethylbenzonitrile. By mass spectrometry based onMALDITOF-MS, the result was consistent with the molecular weight(Calcd.: 360.05, Found: 360.38) of the compound (121).

Synthesis Example 4

An exemplified compound (131) was yielded in the same way as inSynthesis Example 1 except that 3-chloro-4-methylbenzonitrile was usedinstead of 4-trifluoromethylbenzonitrile. By mass spectrometry based onMALDITOF-MS, the result was consistent with the molecular weight(Calcd.: 384.04, Found: 384.33) of the compound (131).

Asymmetric ones out of the exemplified compounds can be synthesized by,for example, a synthesis method disclosed in Tetrahydron, 2002, vol. 58,p. 5547, or Japanese Patent Application Laid-Open No. 7-21122.

Synthesis Example 5

2.0 g of a compound D illustrated below, 1.8 g of4-trifluoromethylbenzonitrile, and 1.8 g of sodium butoxide weredissolved into 50 g of amyl alcohol, and then the solution was refluxedfor 8 hours. The solution was cooled, and then acetic acid was addedthereto. The solution was stirred for 30 minutes, and then theprecipitation was filtrated and washed with acetic acid and methanol toyield 1.6 g of an exemplified compound (108). By mass spectrometry basedon MALDITOF-MS, the result was consistent with the molecular weight(Calcd.: 356.08, Found: 356.83) of the compound (108).

The compound D was synthesized in accordance with a synthesis methoddisclosed in Synthetic Communication, 1988, vol. 18, p. 1213,Tetrahedron, 2002, vol. 58, p. 5547, or Japanese Patent ApplicationLaid-Open No. 7-53711.

Synthesis Example 6

An exemplified compound (106) was yielded in the same way as inSynthesis Example 5 except that 2,3,4,5,6-pentafluorobenzonitrile wasused instead of 4-trifluoromethylbenzonitrile. By mass spectrometrybased on MALDITOF-MS, the result was consistent with the molecularweight (Calcd.: 378.04, Found: 378.09) of the compound (106).

Next, the above-mentioned compounds and others were each used as anorganic semiconductor material to produce organic transistor devicesindependently by the following two methods:

(1) Formation Method at a Low Vapor-Deposition Rate

Specifically, a thermally oxidized layer was formed as a gate insulatinglayer on a Si wafer having a resistivity of 0.02 Ωcm as a gateelectrode. Thereafter, the resultant was surface-treated withhexamethyldisilazane (HMDS). Moreover, a glass substrate surface-treatedwith hexamethyldisilazane (HMDS) was prepared forretardation-measurement. By vacuum vapor-deposition (vacuum pressure:2.2×10⁻⁶ Torr, vapor-deposition rate: 0.01 to 0.02 nm/sec), somecompounds shown in Table 2 were each stacked thereon into a thickness of110 nm. Furthermore, a mask was used to vapor-deposit gold onto thesurface of the film on the Si wafer to form a source electrode and adrain electrode. In this way, each of organic transistor devices 47 to72 was produced wherein the film thickness of the source electrode andthe drain electrode was 300 nm, the channel width (W) was 3 mm, and thechannel length (L) was 25 μm.

(2) Formation at a High Vapor-Deposition Rate

Some organic semiconductor materials shown in Table 2 were each used toproduce organic transistor devices 73 to 81 independently in the sameway as in the formation method at the low vapor-deposition rate exceptthat the average vapor-deposition rate in the vacuum vapor-depositionwas set into the range of 1.3 to 1.5 nm/sec.

Comparative Examples 4 and 5

The compound B used in Comparative Example 2 was used as an organicsemiconductor material to produce organic transistor devices by twomethods, wherein the vapor-deposition rate was varied, respectively(Comparative Example 4: the vapor-deposition rate was from 0.01 to 0.02nm/sec; and Comparative Example 5: the vapor-deposition rate was from1.3 to 1.5 nm/sec).

The organic transistor devices produced as described were each used, andthe transistor device was stored at 60° C. in the atmosphere. Changes ofthe transistor characteristic of the device with the passage of timewere compared. A voltage of 50 V or −50 V was applied between the sourceelectrode and the drain electrode, and a sweep of voltages ranging from50 to −50 V was made onto the gate electrode. The ratio of the maximumcurrent value (ON current) between the source electrode and the drainelectrode at this time to the minimum current value (OFF current)therebetween was defined as the ON/OFF ratio. About each of the devices,the ON/OFF ratio just after the formation of the device was regarded asone. In this case, the relative value of the ON/OFF ratio after one day,that after one week, and that after one month are as shown in Table 2.

Next, the glass substrates formed for the device numbers 47 to 81 inExample 2, and the glass substrates in Comparative Examples 4 and 5 wereeach used to measure the retardation in the wavelength range of 400 to700 nm by means of an ellipsometer (M-220, manufactured by JASCO Corp.).

One example of the measurement results is shown in FIG. 2 in case of thecompound 108 (the device numbers 50 to 74 in Example 2). According toFIG. 2, a remarkable difference was shown at a longer wavelength side(at about 600 to 700 nm) from the absorption end of the compound. Incase of the device number 74, the absolute value of the retardation wasabout zero; however, in case of the device number 50, a value of 4 to 8degrees was shown. The difference has not been made clear; however, itappears that the difference was probably based on the arrangement of thecompound or the order of the arrangement in the vapor-deposited film. InTable 2, “Absolute value (degrees) of the retardation” represents thevalue at 650 nm, where the compound exhibited no absorption.

TABLE 2 Absolute value Organic of the Element Semiconductor retardationRelative value of the ON/OFF ratio No. material (degrees) One day later7 days later 30 days later 47 Compound(101) 6.22 0.98 0.92 0.92 48Compound(105) 5.89 0.97 0.94 0.91 49 Compound(106) 5.99 0.97 0.91 0.8750 Compound(108) 5.69 0.98 0.93 0.89 51 Compound(113) 5.22 1.00 0.920.88 52 Compound(117) 6.34 0.95 0.89 0.90 53 Compound(133) 3.22 0.910.85 0.82 54 Compound(138) 8.33 0.97 0.91 0.90 55 Compound(146) 6.220.98 0.90 0.86 56 Compound(156) 2.28 0.92 0.84 0.81 57 Compound(172)3.09 0.91 0.87 0.80 58 Compound(178) 2.55 0.93 0.83 0.82 59Compound(180) 5.27 0.96 0.90 0.89 60 Compound(184) 6.53 0.99 0.90 0.8761 Compound(190) 4.96 0.92 0.88 0.81 62 Compound(191) 3.11 0.92 0.840.82 63 Compound(200) 5.38 0.96 0.91 0.91 64 Compound(203) 6.77 0.970.88 0.86 65 Compound(205) 5.24 0.98 0.90 0.89 66 Compound(222) 6.380.97 0.91 0.86 67 Compound(226) 5.82 0.96 0.93 0.90 68 Compound(236)5.36 0.98 0.89 0.86 69 Compound(239) 6.85 0.98 0.88 0.85 70Compound(242) 5.68 0.96 0.92 0.89 71 Compound(252) 6.85 0.97 0.93 0.9072 Compound(254) 5.24 0.96 0.95 0.96 73 Compound(104) 0.54 0.92 0.760.67 74 Compound(108) 0.13 0.80 0.68 0.40 75 Compound(124) 0.17 0.960.79 0.71 76 Compound(130) 0.51 0.93 0.79 0.76 77 Compound(139) 0.820.92 0.74 0.59 78 Compound(190) 0.39 0.93 0.80 0.64 79 Compound(228)0.42 0.91 0.77 0.60 80 Compound(229) 0.73 0.96 0.82 0.72 81Compound(242) 0.69 0.92 0.78 0.64 Comparative Compound B 2.64 0.91 0.56— Example 4 Comparative Compound B 1.02 0.89 0.33 — Example 5

In the table, the symbol “---” means that the compounds were not drivenas a transistor. Each of the retardations was measured by the use of the“M-220” manufactured by JASCO Corp.

In the device numbers 47 to 72 shown in Table 2, the absolute value ofthe retardation was 1 degree or more. On the other hand, in the devicenumbers 73 to 81, the absolute value of the retardation was 1 degree orless. This was affected by the difference in the vapor-deposition rate.The device numbers 47 to 72 are recognized to have higher relativevalues of ON/OFF ratio after 30 days and an excellent stability overtime comparing to the device numbers 73 to 81.

Furthermore, it has been understood that Comparative Examples 4 and 5were not driven as a transistor after 30 days. These semiconductor thinfilms were not a uniform film, and a phenomenon such as aggregation wascaused in their surfaces.

As described above, in a case where organic semiconductor materialsknown in the prior art stand still in the atmosphere, thin filmstherefrom are doped with oxygen or the like, so that characteristicsthereof deteriorate. It is known that the compounds themselves start todeteriorate in some cases. However, it is understood that any organictransistor device produced by the use of the semiconductor material ofthe invention in its active layer exhibits a high stability over time inthe atmosphere also.

1. An organic transistor having a source electrode, a drain electrode, agate electrode, and an organic semiconductor layer, wherein the organicsemiconductor layer comprises a compound represented by general formula[1]:

wherein A and B each independently represent a substituted alkyl group,an unsubstituted alkyl group, a substituted heterocyclic group, anunsubstituted heterocyclic group, a substituted aryl group, or anunsubstituted aryl group.
 2. The organic transistor according to claim1, wherein A and B are independently represented by general formula [2]:

wherein R¹ to R³ each independently represent a hydrogen atom, a halogenatom, a substituted alkyl group, an unsubstituted alkyl group, asubstituted heterocyclic ring, an unsubstituted heterocyclic ring, asubstituted aryl group, unsubstituted aryl group, a substituted alkoxygroup, an unsubstituted alkoxy group, a substituted heterocyclic oxygroup, an unsubstituted heterocyclic oxy group, a substituted aryloxygroup, an unsubstituted aryloxy group, an alkylthio group, an arylthiogroup, a heterocyclic thio group, an alkylsulfonyl group, anarylsulfonyl group, a heterocyclic sulfonyl group, a substituted aminogroup, or an unsubstituted amino group; and substituents of R¹ to R³ maybe bonded to each other to form a cycloalkyl ring, a heterocyclic ring,or an aromatic hydrocarbon ring.
 3. The organic transistor according toclaim 1, comprising the source electrode, the drain electrode, the gateelectrode, and the organic semiconductor layer, wherein the organicsemiconductor layer is formed by vacuum vapor-deposition at avapor-deposition rate of 1 nm/sec or less.
 4. The organic transistoraccording to claim 1, further comprising a gate insulating film.
 5. Anorganic transistor comprising a source electrode, a drain electrode, agate electrode, and an organic semiconductor layer, wherein the organicsemiconductor layer comprises a compound represented by general formula[3]:

wherein R¹ to R¹⁰ are each independently a hydrogen atom, a halogenatom, an alkyl group which has 4 or less carbon atoms, an alkyl groupwhich has 4 or less carbon atoms that is substituted with a halogenatom, an alkoxy group which has 4 or less carbon atoms, an alkoxy groupwhich has 4 or less carbon atoms that is substituted with a halogenatom, an amino group which has 4 or less carbon atoms, an amino groupwhich has 4 or less carbon atoms that is substituted with a halogenatom, a nitro group, or a cyano group, and the compound contains atleast one halogen atom.
 6. The organic transistor according to claim 5,wherein R⁷ to R¹⁰ are independently a hydrogen atom or a halogen atom.7. The organic transistor according to claim 5, wherein the halogen atomis a fluorine atom.
 8. The organic transistor according to claim 5,comprising the source electrode, the drain electrode, the gateelectrode, and the organic semiconductor layer, wherein the organicsemiconductor layer is formed by vacuum vapor-deposition at avapor-deposition rate of 1 nm/sec or less.
 9. The organic transistoraccording to claim 5, further comprising a gate insulating film.
 10. Aprocess for producing an organic transistor comprising a sourceelectrode, a drain electrode, a gate electrode, and an organicsemiconductor layer, comprising subjecting a compound represented bygeneral formula [1] or [3] to vacuum vapor-deposition or spin coating,to form an organic semiconductor layer

wherein A and B independently represent a substituted alkyl group, anunsubstituted alkyl group, a substituted heterocyclic group, anunsubstituted heterocyclic group, a substituted aryl group, or anunsubstituted aryl group

wherein R¹ to R¹⁰ are independently a hydrogen atom, a halogen atom, analkyl group which has 4 or less carbon atoms, an alkyl group which has 4or less carbon atoms that is substituted with a halogen atom, an alkoxylgroup which has 4 or less carbon atoms, an alkoxy group which has 4 orless carbon atoms that is substituted with a halogen atom, an aminogroup which has 4 or less carbon atoms, an amino group which has 4 orless carbon atoms that is substituted with a halogen atom, a nitrogroup, or a cyano group, and the compound contains at least one halogenatom.
 11. The process for producing an organic transistor according toclaim 10, wherein the organic semiconductor layer is formed by thevacuum vapor-deposition wherein the rate of the vapor-deposition is setto 1 nm/sec or less.